1. Field of the Invention
The present invention relates to a vehicle seat having an active head rest.
2. Description of the Related Art
There is a vehicle seat that adopts an active head rest of moving a support portion of a head rest to a front side and an upper side instantaneously in back collision (back face collision) of a vehicle. An active head rest supports the head of a passenger in back collision and alleviates whiplash. In a head rest of this kind, it is important how swiftly the head can be received by the support portion in back collision. For that purpose, it is necessary to make the support portion swiftly reach a collision corresponding position. When a time period from bringing about back collision until the head collides with the support portion can be shortened, an amount of moving the head to a rear side is reduced by that amount. Thereby, whiplash disease can further be reduced. As means therefor, for example, it is conceivable to increase a speed of moving the support portion. However, there is a limit to some degree in increasing the speed of moving the support portion. Hence, as a vehicle seat enabling a support portion to be swiftly proximate to the head by improving a locus of moving the support portion, there is U.S. Pat. No. 6,631,955.
According to U.S. Pat. No. 6,631,955, as shown by FIG. 13, a stay 101 of a head rest 100 is inserted into a support 102. As a result of a back collision, the stay 101 is moved to an upper side while being brought into sliding contact with an inner face of the support 102. Thereby, a support portion 105 is moved from an initial position to a collision corresponding position integrally with the stay 101 while maintaining an angle relative to the stay 101. A locus of moving the support portion 105 is defined by a shape of the stay 101 relative to the inner face of the support 102. Specifically, the locus is constituted by a first locus T1 of first moving in a front upper direction to some degree while maintaining an attitude angle of the initial position by the support portion 105, and a second locus T2 of moving to the upper side while being inclined such that an upper portion of the support portion 105 rises out successive to the first locus T1. By defining the first locus T1 in this way, the support portion 105 is made to be proximate to the head of a passenger as swiftly as possible.
However, the support portion 105 tracking the first locus T1 is only moved in the front upper direction while maintaining the attitude angle at the initial position. Therefore, a final point of the first locus T1 does not reach a final collision corresponding position. Thereby, there is a time lag in making the support portion 105 reach the collision corresponding position proximate to the head the most from the final point of the first locus T1. That is, there is a constant distance between a collision point P1 at which the head collides with the support portion 105 in moving on the second locus T2, and a collision point P2 at which the head collides with the support portion 105 at the final collision corresponding position constituting the final point of the second locus T2. Therefore, there is a case in which the head of the passenger collides with the support portion 105 before the support portion 105 reaches the collision corresponding position, and a time period until the head collides with the support portion 105 from bringing about a back collision, is not stabilized. Therefore, also a degree of an injury by whiplash is not stabilized.
Thus, there is a need in the art for a vehicle seat capable of receiving the head at a timing equivalent to that of a final collision corresponding position even in the midst of relatively moving a support portion.